Question

A student explains the formation of the planetary system as follows.
"The birth of the planetary system begins with a rotating cloud called nebula which contains hot gases. When these gases cool, the nebula expands and becomes a flattened disk. Gravitational force causes rings of gases to be left behind when the nebula expands. At the center of the nebula, the gases combine to form the sun and the planets form in the outer flattened portion of the disk.

What is the flaw in the students explanation?

A. The nebula contracts and shrinks instead of expanding
B. The gases in the nebula get heat